Grounding Victron Confusion

[Ronaldrwl]

I'm reading the manual for a Victron MPPT 150 - 45 SmartSolar Charge Controller. I just would like clarity on grounding. In the manual is says don't connect the charger to a grounded PV array. I must not understand that statement. I have a combiner box with a ground and lightning protection. Is this a problem? Here is a snippet from their manual:

4.4. Grounding
Battery grounding
The solar charger can be installed in a positive or in a negative grounded system.
Apply a single ground connection, preferably close to the battery, to prevent system issues or ground loops.
Chassis grounding
A separate ground path for the chassis ground is permitted because the chassis is isolated from the positive and the negative terminals.
PV array grounding
The positive and negative of the PV array should not be grounded.
Ground the frame of the PV panels to reduce the impact of lightning.
Do not connect the solar charger to a grounded PV array. Only one ground connection is allowed, and this should be near the battery.

 

[MichaelK]

You can think of grounding as protection against two different things. Either lightning protection, or touching shock protection. It's common for ground-mounted panels to be grounded to the frame that goes straight into the earth below it. Roof-top panels would get grounded to a ground rod placed in the earth somewhere below the panels.

This is supposed to be separate from the grounding that is made for all your household electrical appliances, wall-sockets, grounded motors, ect. That is typically a ground rod pounded in the earth somewhere close to where your main electrical panel is. It might also be a well-casing, metal water pipes in the ground, or the steel rebar of your foundation.

Part of this is terminology confusion. Just for the sake of this discussion, let's call each component an earthing element. There are going to be below-ground earthing elements, and above-ground earthing elements. Below-ground earthing elements are things like the ground rod(s), water pipes, steel rebar, ect, that are physically in contact with the ground. Above-ground earthing elements include the ground wiring, grounding bussbar, wall/switch sockets, ect.

The above-ground earthing elements may all be serially connected together, and the below-ground earthing elements can all be serially connected together, but the above-ground elements and below-ground elements can meet together at one and only one location, usually the main electrical panel.

This is a very specific code requirement. Connecting the solar array to the building round would create a "loop" of grounding wire and violate the "one and only one" rule mentioned above. That would create a lightning attracter, which would be considered dangerous.

 

[sunshine_eggo]

deleted

 

[Ronaldrwl]

Thank you for taking the time to help!
I interpret this as:
Ground the Panels to it's own earth ground.
Ground the CC to the house ground?

 

[MisterSandals]

Ground the CC to the house ground?

If your SCC is not otherwise connected to the "house ground" (meaning electrical grid circuitry?), then i would opt to NOT connect to that but rather to plumbing or something that will likely never carry a ground fault or other current.

 

[khajiit]

Hello

Sorry for the thread revival, I came here to ask the same question.

I'm living in Spain, on the top floor of a 4 story block of flats. Im allowed to have panels on my private terrace, but not on the roof on top of my flat, even though i'm in the top flat, as it's considered communal. Anyway, I will probably get a victron 100/20, but was reading the manual, and then found this thread, and had similar questions.

I had interpreted the Victron statements to mean.

• Ground the frame of the PV panels to reduce the impact of lightning. (ground the frame ~ to where im not sure now)
• Do not connect the solar charger to a grounded PV array. (do not ground the panels to the grounded frame? maybe!?)

Having read the thread i'm even more confused. Did some plumbing work when i used to live in the UK, a ground wire was always there and evident, and copper pipes ran external to the walls.

Here in spain the flat is newer, and not a copper pipe in sight. just those stainless steel flexible pipe connectors to the taps and all the pipes are embedded into the walls. I checked my metal kitcthen sink and no ground wire, just clipped onto what I assume is marble worktop. Also the guttering is aluminium or painted light steel, but I can't see any ground wire, just screwed into the wall, soffits and fascias.


So for the panels and the mppt I have no idea what I'm supposed to do. so came asking for help.

 

[alejnavab]

Hello

Sorry for the thread revival, I came here to ask the same question.

I'm living in Spain, on the top floor of a 4 story block of flats. Im allowed to have panels on my private terrace, but not on the roof on top of my flat, even though i'm in the top flat, as it's considered communal. Anyway, I will probably get a victron 100/20, but was reading the manual, and then found this thread, and had similar questions.

I had interpreted the Victron statements to mean.

• Ground the frame of the PV panels to reduce the impact of lightning. (ground the frame ~ to where im not sure now)
• Do not connect the solar charger to a grounded PV array. (do not ground the panels to the grounded frame? maybe!?)

Having read the thread i'm even more confused. Did some plumbing work when i used to live in the UK, a ground wire was always there and evident, and copper pipes ran external to the walls.

Here in spain the flat is newer, and not a copper pipe in sight. just those stainless steel flexible pipe connectors to the taps and all the pipes are embedded into the walls. I checked my metal kitcthen sink and no ground wire, just clipped onto what I assume is marble worktop. Also the guttering is aluminium or painted light steel, but I can't see any ground wire, just screwed into the wall, soffits and fascias.


So for the panels and the mppt I have no idea what I'm supposed to do. so came asking for help.

Some general clarifications about grounding:

• Equipment grounding refers to connecting to earth ground the enclosure of equipment, as well as metallic raceways, etc.
• System grounding refers to connecting to earth ground a current-carrying conductor, usually the neutral wire for AC systems and the negative wire for DC systems.

The Victron manual is referring to not connect a PV array (positive and negative wires, forget about the frames) that is grounded, to a solar charge controller, if the battery bank is also grounded, because the negative terminal of the PV side of the SCC is directly connected to the negative terminal of the DC (battery) side of the SCC.

If you connect a grounded PV array (say, negative wire is grounded) to a SCC where the battery bank is also grounded (say, the negative wire), then, because the input and output negatives of the SCC are solidly connected internally, you will have created two connections between negative and ground. It’s like when you ground twice a neutral wire, or when you connect the neutral to the casing in subpanels (recall the neutral is already connected to the casing in the main panel): you create a parallel path for normal current to flow, i.e. a ground loop. Which can be dangerous.

For the same reason, in the US, you must not ground the neutral wire of a genset, if the ATS does not interrupt the neutral. The reason is because the utility neutral is already grounded, so providing a second ground connection creates a ground loop.